In recent years, there have been known outboard engine units of a type in which a lower half section of an engine room is defined by a lower cover composed of resin-made left and right (i.e., port- and starboard-side) cover members (e.g., Japanese Patent Application Laid-Open Publication Nos. 2004-338463 and 2001-199393 which will hereinafter be referred to as patent literature 1 and patent literature 2, respectively).
In the outboard engine unit disclosed in patent literature 1, the left and right cover members of the lower cover are bolted together in directly-abutted relation to each other. In the outboard engine unit disclosed in patent literature 2, an under cover (i.e., lower cover) is fixed to an engine body, and left and right cover halves (i.e., left and right cover members) of the under cover are bolted together in abutted relation to each other.
With both of the outboard engine units disclosed in patent literature 1 and patent literature 2, it is necessary to position a fixed section of the body of the outboard engine unit close to respective abutting portions of the left and right cover members, in order to reliably achieve appropriate abutment between the abutting portions of the cover members; actually, the left and right cover members are fastened together by common bolts passed through their respective abutting portions and fixed section.
However, with the aforementioned conventionally-known outboard engine units, when one of the left and right cover members is removed or detached for desired maintenance work, fixation of the other cover member would become unstable. Thus, in re-assembling of the cover, properly positioning the left and right covers etc. would require a considerable time and labor, which disadvantageously results in poor workability.
In the aforementioned conventionally-known outboard engine units, there are further provided an auxiliary exhaust outlet for discharging a portion of engine exhaust to the outside, and a water pilot hole for discharging a portion of engine cooling water to the outside of the engine room. Sealing structure for sealing the auxiliary exhaust outlet is attached to either or both of the abutting portions of the port-side and starboard-side cover members. Thus, when any of the cover members is to be detached, it is also necessary to detach the sealing structure, and thus, the detaching operation and subsequent re-assembling operation would become cumbersome, which disadvantageously result in poor workability. Further, a tube of the water pilot hole (hereinafter “water pilot tube”) etc. are supported directed by the left and right cover members. Thus, when any of the cover members is to be detached, there arises a need to detach the water pilot tube, and thus, the detaching operation and subsequent re-assembling operation would become cumbersome, which also disadvantageously result in poor workability.
There have also been known outboard engine units of a type in which the axis of engine cylinders is offset relative to the axis of a crankshaft (e.g., Japanese Patent Application Laid-open Publication No. 2001-115817, which will hereinafter be referred to as patent literature 3). According to the disclosure of patent literature 3, the engine cylinder axis is offset relative to the crankshaft axis by a predetermined distance in a direction where a thrust force acts on a piston. Ignition plug is provided on the inner surface of a cylinder head. Thus, in order to secure a sufficient space for performing maintenance work of the ignition plug, it is necessary to
(a) increase the size of a bottom cowling (i.e., lower cover) to thereby secure a sufficient space within the bottom cowling, or
(b) lower the lower end position of a top cowling (i.e., engine cover) so that the ignition plug is exposed sideways when the top cowling is removed.
If the above (a) option is taken, the increased size of the bottom cowling leads to an increased size of the top cowling because the bottom cowling and top cowling are vertically joined together in edge-to-edge abutted relation, with the result that the overall size of the outboard engine unit and weight of the top cowling would significantly increase. Further, if the above (b) option is taken, lowering the lower end position of the top cowling leads not only to an even greater concave depth of the top cowling, having a deep bowl shape, but also to an increased size and weight of the top cowling, as a result of which operation for detaching the top cowling tends to be cumbersome and troublesome.
Generally, the outboard engine units employ a vertical engine with a vertically-oriented crankshaft and horizontally-oriented cylinders; especially, the high-power outboard engine units employ a four-stroke engine with a plurality of cylinders. In such outboard engine units, a plurality of cylinders (e.g. four cylinders in the case of a four-cylinder engine) are disposed in a vertical arrangement with a great vertical interval between the uppermost cylinder and the lowermost cylinder. With such plural-cylinder engines, the engine body unavoidably has an increased vertical length, as a result of which the bow-shaped top cowling tends to have an even greater depth.